1. Field of the Invention
The present invention relates to test diaphragms for the electrical probing of integrated circuits and the like.
2. Prior Art
In certain situations it is desired to be able to directly probe an integrated circuit by probing the lead wire pads on the chip itself for test purposes. By way of example, during manufacture of integrated circuits, mechanical probes are used to successively probe each integrated circuit in a predetermined matrix of integrated circuits fabricated from a single silicon wafer. In other situations, such as in the fabrication of hybrid circuits and high density multi-chip interconnect (HDMI) circuits, it is also often desired to be able to probe an integrated circuit for test purposes, either to exercise and test a single integrated circuit, or possibly to temporarily interconnect to one or more other integrated circuits to test the cooperation thereof.
It is particularly desirable to be able to test semiconductors at their operating clock speed. Standard probes are too slow. Because the probes physically act as antennas, the speed of testing is very limited. Therefore the current conventional method of probing a semiconductor does not guarantee its operation at its rated or potential speed. Usually a complex semiconductor is tested at full speed only after the packaging is completed.
In the case of multichip modules, the multiplicity of chips and complexity of the circuits in a package makes it necessary to test the components separately before assembly. This is one of the main advantage over wafer scale integration, i.e. the ability to test the substrate and the chips individually before assembly therefore eliminating the need for redundant circuits in case of failure of one of the components to perform as expected.
In the near future, as production volume of multi-chip modules builds-up, it will be very useful, even crucial, to do the evaluation of the chips before assembling the package in a multichip module. No method, other than the diaphragm, allows the proper testing of chips because of the speed problem, but the ability to build diaphragms to test the substrate circuits may also become important because of the number of points to test in a short a time as possible. The diaphragm allows the construction of very complex structures which will avoid the current necessity of testing with flying probes and the inherent speed limitations of mechanically moving probes. Accordingly, in such instances much lower cost and specialized probing has been achieved in the past using specially fabricated diaphragms having electrical contacts and associated circuitry on one surface thereof, and supported so as to be responsive to air pressure on the opposite side thereof to encourage the contacts against the lead wire pads on an integrated circuit positioned parallel to and immediately adjacent the first surface of the diaphragm. Such test diaphragms have the advantage of potentially being low cost and potentially readily fabricatable in different forms for a variety of probing applications and circuits. In practice however, prior art fabrication techniques for fabricating such diaphragms were less then ideal, resulting in poor yield and lack of repeatability diaphragm to diaphragm.
In particular, in accordance with prior art techniques, such diaphragms are fabricated by putting the probing circuitry down on a film of suitable diaphragm material, such as mylar or the like, using conventional electroplating or sputtering deposition and photolithographic processes. At this stage of fabrication, the probe circuit could readily be made with the desired accuracy. However, the next step, specifically the mounting of the diaphragm onto a typical diaphragm support and the interconnecting of the circuit on the diaphragm to contact points on the support, is fundamentally a hand operation neither readily controlled nor repeatable in results. Accordingly, one of the purposes of the present invention is to maintain the potential advantages of test diaphragms, namely their relatively low cost and convenience, yet make the fabrication thereof an orderly process having accuracies throughout consistent with modern photolithographic processes and substantially free of the manual fabrication steps which give rise to inconsistencies and/or inaccuracies in the completed ready to use test diaphragms.